Just watched No Country For Old Men. Fantastic film. Anyway, I've been watching quite a few of these kinds of films recently; based around the barren landscape of cowboy country.
The characters portrayed all have a distinctly Delta air to them. No ambition, slow speech, movement and same routine everyday, where nothing happens. "Quiii't lil' town we gaht here" feel to them. I'd say most of the inhabitants of these little towns, motels and convenience stores are SLIs.